Field of the Invention
The present invention relates to a comparator circuit having automatic offset correction function between a plurality of comparators, a power supply control IC using the comparator circuit, and a switching power supply device.
Description of Related Art
Conventionally, there is known a comparator circuit in which a plurality of comparators having different characteristics are selectively used according to a situation.
However, in a conventional comparator circuit, if the comparators have different input offsets, logical switching timing of comparison signal is different between the comparators even if the same input signal is compared with the same reference voltage. As a result, there is a problem that an output accuracy of the entire comparator circuit is deteriorated.
In order to solve the problem described above, it is effective to perform a correction process for eliminating the difference between input offsets of the comparators. However, if the correction process is performed only when the comparator circuit is activated, there is a problem that input offsets of the comparators may differ from each other due to change in external environment (for example, power supply voltage, temperature, or the like) after the correction process. In addition, if the correction process is performed only when the comparator circuit is activated, there is also a problem that if inappropriate correction is performed in the correction process when it is activated, different input offsets of the comparators are kept.
Note that the offset adjusting method disclosed in JP-A-2010-35140 has a structure in which output of the first comparator is compared with output of the second comparator, and offset amounts having opposite polarities are set to the comparators according to a result of the comparison, and the structure is essentially different from the structure of the present invention.